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Old June 23rd, 2019, 11:42 AM #1
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STI Mag Tuning

Got three new generation STI mags with my 2011 build. All were tuned by the gunsmith and run fine. I purchased 2 more of the same mags and they also run good 99% of the time, however I am having an issue with them when reloading on an open chamber (only during a match of course because I typically slam the mag in to make sure it is seated. When I do this, and hit the slide release, the round will not chamber unless I man handle the slide. I also can not drop the mag and the mag release is half way pushed in all by itself (as if the mag is over inserted. It is easy to see that the bullet has moved forward in these cases and obvious to me that the feed lips need to be adjusted.

Problem is, I have no idea how to go about doing this nor do I have any special tools to make it happen. Any help, opinions, ideas?
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Old June 23rd, 2019, 03:50 PM #2
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I think you may already be on to the problem. From what you describe, it does sound like the mag is going in too far. The slide is probably dragging on the top of the mag and causing the feed issue. I would examine the mag catch slot on the mags, comparing them to the mags that do work. I would check the mag catch as well as the catch tension for any obvious issues while at it.
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Old June 23rd, 2019, 04:48 PM #3
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Measure the dimensions of the different magazines. You have a caliper?
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Old June 23rd, 2019, 04:51 PM #4
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Quote:
Originally Posted by jimbobborg View Post
Measure the dimensions of the different magazines. You have a caliper?
I need to get a digital caliper so that I can read it. The one I have is just too small for my eyes.
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Old June 23rd, 2019, 05:03 PM #5
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http://www.brazoscustom.com/Home.htm
ďSlide Lock Back or Not?

by Bob Londrigan, published in Front Sight Magazine, May 2005

Why do I set up my competition guns to not lock back after the last round? Since I often hear that question, I thought I would go over the proís and conís of having a gun lock or not lock back. Then Iíll explain the best way to make this type of modification to your gun.

The stock 1911 is designed so that the slide locks open after the last round in the magazine has been fired. This happens because the slide stop engages a pad on the magazine follower that pushes the slide stop up into a detent in the slide. Most 1911 users view this as a desirable feature because you can chamber another round and be ready to go just by inserting another magazine and releasing the slide stop. However, when competing with 2011 style guns there are some disadvantages to this system Ė enough so that I prefer to disable this feature in the competition guns I build.

The magazine setup that I prefer uses a Grams follower. This follower (as are most other aftermarket followers) is designed to sit up as high in the magazine as possible in order to maximize magazine capacity. Increased capacity is good, but a side effect is that a high-positioned follower may cause the slide to lock back prematurely with one round left in the magazine. This can be adjusted out but it can be a tedious and unreliable process. If the slide is set to not lock back, then this problem is avoided and you can still benefit from maximum capacity.

Reloading the gun while the slide is locked back with your adrenaline pumping in the middle of a stage can have some disastrous results. In 2011 style guns, you can actually over insert the magazine when the slide is locked back. This jams the magazine in the gun. Realize that you are pushing a wedge shaped object (the magazine) into a hole (the magwell) that is narrow at the top. As a result, it may wedge itself in and then be hard to remove. Over inserting the magazine can also break the tip off your ejector if you have an extra long ejector that hangs over the magazine well. The top of the magazine will contact the ejector because it no longer has the bottom of the slide to stop it. Thus, it pushes up on the ejector sometimes with enough force to snap it off.

The best way to set up your magazine to not lock back is to modify both the slide stop and the follower. To begin, drill a small detent in the slide stop to engage the slide stop plunger. This keeps the slide stop from moving up or out in the event it is bumped by the nose of a bullet. Use an extra long drill or a dremel tool with a small carbide ball bit to make the detent. Then modify the ledge on the slide stop as shown in Figure 1 (the slide stop on the left has been modified). You want to trim it flat but leave enough material so it wonít break. Be sure not to take off any of the height.



Figure 1

If you modify only the slide stop, the tab on the follower may still jam on the slide stop causing magazines to stick or your gun to malfunction. Therefore, you also need to modify the ledge on the follower. I like to trim the ledge down at a 45-degree angle as shown in Figure 2. This keeps the follower out of the way of the slide stop and keeps it from binding.



Figure 2

After you have modified your slide stop and follower, test fire the magazine to see if the slide locks back or if anything binds. It should not. If it does, check your follower and take a little more off the ledge.

On the flip side of the issue, competitors have various reasons for wanting to set up their gun to lock back. For example, you might want this to shoot limited 10 or IDPA. In this case, you have two choices: You can either switch back to stock followers, or you can modify your after-market followers to ensure consistent last round lock back. Since the lock-back ledge on stock followers usually sits a little lower, they generally work fine with a slide that locks back early. You can switch to a factory follower if you are shooting limited 10 or IDPA because maximum round count is not a priority.

To modify your aftermarket followers to ensure you gun does not lock back occasionally with one round left in the magazine try the following solution: First, put a detent in the slide stop. This will help prevent the slide stop from engaging and will often solve the problem. If it does not, then you are going to have to either modify the pawl on the slide stop or modify each of the after-market followers. Work on the slide stop pawl first to raise it a little. Take material off the bottom (raise the engagement surface). This may solve the problem with most of the followers. If it does not, then work on each of the offending followers. One word of caution before you start working on the followers - make sure the lips on the magazines are tuned to the proper dimensions. Opening or closing the dimension on the lips affects how high the follower sits and, thus, affects the lockback. Begin by modifying the ledge as shown in figure 3. I like to use a dremel tool with a 5/16 cylinder bit to take down the ledge. Take off just a little at a time and then test it. With three rounds in your magazine, shoot the gun until it is empty. If necessary, take a little more off the ledge and then test again. Repeat as needed until you get it right, and then repeat it a few more times to make sure lock back is consistent. When you have one follower working properly, copy the setup on any other mags that donít work



Figure 3

To lock back or not to lock back is a personal choice based on your shooting style and preferences. Whichever way you choose, the important thing is that your gun does the same thing every time. Only then can you depend on it in a match.Ē
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Old June 23rd, 2019, 05:53 PM #6
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Quote:
Originally Posted by dbledoc View Post
http://www.brazoscustom.com/Home.htm
ďSlide Lock Back or Not?

by Bob Londrigan, published in Front Sight Magazine, May 2005

Why do I set up my competition guns to not lock back after the last round? Since I often hear that question, I thought I would go over the proís and conís of having a gun lock or not lock back. Then Iíll explain the best way to make this type of modification to your gun.

The stock 1911 is designed so that the slide locks open after the last round in the magazine has been fired. This happens because the slide stop engages a pad on the magazine follower that pushes the slide stop up into a detent in the slide. Most 1911 users view this as a desirable feature because you can chamber another round and be ready to go just by inserting another magazine and releasing the slide stop. However, when competing with 2011 style guns there are some disadvantages to this system Ė enough so that I prefer to disable this feature in the competition guns I build.

The magazine setup that I prefer uses a Grams follower. This follower (as are most other aftermarket followers) is designed to sit up as high in the magazine as possible in order to maximize magazine capacity. Increased capacity is good, but a side effect is that a high-positioned follower may cause the slide to lock back prematurely with one round left in the magazine. This can be adjusted out but it can be a tedious and unreliable process. If the slide is set to not lock back, then this problem is avoided and you can still benefit from maximum capacity.

Reloading the gun while the slide is locked back with your adrenaline pumping in the middle of a stage can have some disastrous results. In 2011 style guns, you can actually over insert the magazine when the slide is locked back. This jams the magazine in the gun. Realize that you are pushing a wedge shaped object (the magazine) into a hole (the magwell) that is narrow at the top. As a result, it may wedge itself in and then be hard to remove. Over inserting the magazine can also break the tip off your ejector if you have an extra long ejector that hangs over the magazine well. The top of the magazine will contact the ejector because it no longer has the bottom of the slide to stop it. Thus, it pushes up on the ejector sometimes with enough force to snap it off.

The best way to set up your magazine to not lock back is to modify both the slide stop and the follower. To begin, drill a small detent in the slide stop to engage the slide stop plunger. This keeps the slide stop from moving up or out in the event it is bumped by the nose of a bullet. Use an extra long drill or a dremel tool with a small carbide ball bit to make the detent. Then modify the ledge on the slide stop as shown in Figure 1 (the slide stop on the left has been modified). You want to trim it flat but leave enough material so it wonít break. Be sure not to take off any of the height.



Figure 1

If you modify only the slide stop, the tab on the follower may still jam on the slide stop causing magazines to stick or your gun to malfunction. Therefore, you also need to modify the ledge on the follower. I like to trim the ledge down at a 45-degree angle as shown in Figure 2. This keeps the follower out of the way of the slide stop and keeps it from binding.



Figure 2

After you have modified your slide stop and follower, test fire the magazine to see if the slide locks back or if anything binds. It should not. If it does, check your follower and take a little more off the ledge.

On the flip side of the issue, competitors have various reasons for wanting to set up their gun to lock back. For example, you might want this to shoot limited 10 or IDPA. In this case, you have two choices: You can either switch back to stock followers, or you can modify your after-market followers to ensure consistent last round lock back. Since the lock-back ledge on stock followers usually sits a little lower, they generally work fine with a slide that locks back early. You can switch to a factory follower if you are shooting limited 10 or IDPA because maximum round count is not a priority.

To modify your aftermarket followers to ensure you gun does not lock back occasionally with one round left in the magazine try the following solution: First, put a detent in the slide stop. This will help prevent the slide stop from engaging and will often solve the problem. If it does not, then you are going to have to either modify the pawl on the slide stop or modify each of the after-market followers. Work on the slide stop pawl first to raise it a little. Take material off the bottom (raise the engagement surface). This may solve the problem with most of the followers. If it does not, then work on each of the offending followers. One word of caution before you start working on the followers - make sure the lips on the magazines are tuned to the proper dimensions. Opening or closing the dimension on the lips affects how high the follower sits and, thus, affects the lockback. Begin by modifying the ledge as shown in figure 3. I like to use a dremel tool with a 5/16 cylinder bit to take down the ledge. Take off just a little at a time and then test it. With three rounds in your magazine, shoot the gun until it is empty. If necessary, take a little more off the ledge and then test again. Repeat as needed until you get it right, and then repeat it a few more times to make sure lock back is consistent. When you have one follower working properly, copy the setup on any other mags that donít work



Figure 3

To lock back or not to lock back is a personal choice based on your shooting style and preferences. Whichever way you choose, the important thing is that your gun does the same thing every time. Only then can you depend on it in a match.Ē
The builder of my gun originally set it up so that the slide would not lock back on the final shot. When I got it, I was like, WTF, why doesn't this POS lock back. He explained that most of the silk shirt guys don't want it to lock back because they never let their gun run dry to begin with. Well, I asked him to make it lock back and he did.

The very first weekend after I got it back from him, I slammed a magazine in with the slide open. It was definitely over inserted and apparently it bent the ejector, which would not allow the slide to move at all. I sent it in to the builder who said, "I told you so" and then fixed it under warranty for me.

I am a middle of the road amateur at best and like to have my slide lock back because I do run it dry often. I was told to by the Dawson precision mag release as it is designed to not allow for over insertion. I did buy it, and it has kept the ejector from being impacted again.

I think I will call Dawson in the morning and see what they suggest. I cant be the first guy who is shooting a 2011 that is way over his skill level. But the real question here is why does this problem occur only with the two non tuned magazines. They honest look identical, but I need to measure them.
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